Heart Attacks That Kill Without Warning Leave Few Clues

May 11, 1986|By Chicago Tribune

Doctors are on the trail of a silent assassin -- the fatal heart attack that strikes without warning, killing thousands of Americans each year.

Often the victims are people who seem to be in excellent health. Two weeks ago Dave McClain, the University of Wisconsin football coach, died of a sudden heart attack in a sauna after finishing a workout. McClain was 48.

His unexpected death recalled the heart attack that felled Jim Fixx, a marathon runner and author of sports books, in July 1984. Fixx, 52, had just completed a run. Like McClain he had no warning of heart problems.

One in four people who die of heart stoppage never feel pain or other prior symptoms. Doctors now suspect that these ''silent'' heart attacks result from a process similar to the more common coronary disease that causes chest pains and alerts its victims to developing problems.

But doctors still cannot explain how hearts can fail without warning, even over an extended period of time.

The formal medical term for this phenomenon is silent ischemia. Ischemia occurs when the hard-working heart muscle cells become starved for oxygen as the result of restricted blood flow. The ischemia is silent when it does not cause chest pain.

Many people, including some marathon runners, apparently undergo deprivation of oxygen to heart muscle cells for years without knowing it.

Some recent studies suggest that this painless heart problem may even be more prevalent in this country's population than the painful type. As many as 5 million Americans may experience some degree of painless heart problems, experts suspect.

Because of the lack of pain with silent ischemia, only exercise stress testing or electrocardiograph readings can suggest when the problem is present -- and even these tests aren't totally reliable.

Even when silent ischemia is identified, doctors do not agree on whether or how to treat it. Many take a wait-and-see attitude. There have been no large, controlled studies to demonstrate whether treating such people would prevent premature deaths.

In the past, indications of silent ischemia were usually ignored because of the relative unreliability of the tests and because of the unpleasant side effects associated with all available heart medicines, according to Dr. Leon Resnekov of the University of Chicago, who is studying the problem.

''We know there are cases where a person has episodes of silent ischemia over the years, and nothing ever comes of it,'' Resnekov said. ''There is no proof this will lead to an infarction heart attack.''

Nevertheless, Resnekov believes in treating silent ischemia just as if it were causing pain.

Several of the country's leading silent ischemia researchers discussed it at the recent annual meeting of the American Heart Association in Washington and at a related symposium at Georgetown University.

At the Washington discussions, doctors noted that no large controlled scientific studies have been performed to measure and document the health threat posed by silent ischemia.

Researchers cite at least three studies that indicate a diagnosis of silent ischemia is useful in predicting when a patient is at risk of having a heart attack, but some researchers maintain that these studies were not extensive enough to be convincing.

The most dramatic evidence in this field comes from individual case reports, especially on patients who were wearing portable electrocardiographic monitors when they experienced the sudden death.

At the Washington meeting Dr. Carl Pepine of the University of Florida discussed a case where the monitor showed a man had what amounted to a painless heart attack for 2 1/2 hours before dying.

''The death episode was witnessed,'' Pepine said. ''His family was in the room during this time, and during this time period he complained of absolutely no symptoms.''

Pepine cited a study suggesting that 72 percent of measured incidents of silent ischemia occur when patients aren't engaged in strenuous activities, and 35 percent of the events happen when they are sitting down, usually at desks in offices.

Dr. Andrew Selwyn of Harvard University described silent ischemia that had been produced in patients by asking them to mentally subtract numbers and by exposing them to cold temperatures. Cigarette smoking also has been seen as a triggering factor.

Selwyn also reported on a circadian rhythm seen in ischemic events, both painful and painless, with patients showing ''a low level of ischemic activity at night but a burst of ischemic activity in the morning when they get up. Now this settles gently throughout the day to cycle again at night.''

Significantly, the ischemic circadian pattern closely follows the pattern of heart attacks studid by Dr. James Muller and colleagues at Harvard who noted that most attacks occur in the morning.

One fundamental question facing researchers is why some deprivation of oxygen to the myocardium or wall of the heart produces pain in some cass and not in others.

Some physicians have suggested that silent episodes are shorter or of less severity tan painful ones, but there is clinical evidence refuting that in some specific cases.

Another idea is that some defect, probably damaged nerves, in the normal anginal warning system prevent it from functioning. The only evidence supporting this idea is that heart transplant survivors don't experience angina, probably because the necessary nerves are lacking. But there is little evidence supporting the damaged nerve thesis in other patients.